Analysis of bio-briquette preparation from teak tree (Tectona grandis Linn. f)

The government has taken energy deflation seriously and is trying to find solutions by implementing energy efficiency and utilizing renewable energy sources. That action also supports the procedure to save the world from the ongoing climate crisis. One of Indonesia’s potential renewable energy sources is biomass, which can be in the form of plantation waste such as teak branches. Based on the analysis results, charcoal made from teak branches had a carbon content about 62.5968%, so it was pretty potential to be used as raw material for bio-briquettes. In this research, bio-briquette from teak branches' charcoal using tapioca binder has been successfully carried out. The manufacture of bio-briquettes was studied by observing the effect of the size parameters of teak charcoal and binder ratio on the heating value and water content of briquettes. The analysis results showed that these two parameters significantly affected the quality of teak branches' bio-briquette. In the ranking, the particle size was much more significant in influencing the calorific value of bio-briquettes, while the binder ratio had more influence on the water content value. The obtained bio-briquettes' calorific value and water content have met the established standards.


Introduction
Based on the estimated data, the researchers uttered that the reduction rate of global fossil energy reserves reaches four billion tons per year [1]. The world's fossil energy reserves would be exhausted within the next forty years at such a rate. Therefore, the world has made various efforts to reduce dependence on fossil energy by promoting energy efficiency and utilizing renewable energy. This step is also in line with global efforts to deal with the current climate crisis. As stated in the Paris Agreement, the nations agreed to restrict the increase in the global average temperature to a value of 1.5 o C from preindustrial temperatures [2]. As one of the countries that engaged ratify the agreement, Indonesia committed to reducing greenhouse gas (GHG) emissions by 29% under the Business as Usual (BaU) scenario by 2030 [3], [4]. In achieving this target, the government makes a serious effort to increase energy sources other than fossils, namely geothermal, solar, wind, hydropower, marine energy, and bioenergy like biogas, waste, biofuel, and biomass [5].
The potential of Indonesia's biomass can reach 49.81 gigawatts, but only about 445 megawatts have been installed [6]. Biomass energy raw materials can be in the form of agricultural waste. One agricultural waste that has not been utilized is teak tree branches. The teak tree (Tectona grandis Linn. f) is a plant that can grow well in tropical and sub-tropical areas with rainfall of around 1300-3800 mm/year [7]. This plant is spread in almost all regions in Indonesia, with thousands of hectares in one district [8]. Teak plants can absorb CO2, so they have a high enough potential to store carbon. Based on research conducted by Lukito and Rohmatiah [9], a onehectare teak plant can absorb 50.113 tons of CO2, which is equivalent to 13.66 tons/ha of carbon. That study also added that teak plants could produce biomass reaching 27.30 tons/ha, of which the branches alone contributed 6.7% to this number. The wood from the teak plant is in great demand as a material for making furniture because of its durable and robust nature [7]. As for teak branches, the local community usually collects a small portion for direct use as firewood, while the rest becomes rotten and is not used. Meanwhile, it has the potential to be used as raw materials for making bio-briquettes.
Biobriquette is a dense fuel coming from biomass [10], [11]. Biomass that has been processed through the carbonization stage into bio-briquettes has proven to be more advantageous than biomass used directly as fuel. The advantages are more environmentally friendly, easy to transport and store, easy to handle [12], [13], and higher calorific value. Bio-briquette, as one of the renewable energy sources, is expected to support the household energy needs and collaboratively reduce the use of coal in the industrial sector, such as steam power plants. Some biomasses have been utilized as materials for making briquettes, such as coconut shell, durian skin [14], corncob, rice husk [12], tree leaves and bamboo [13] and palm kernel shells [15]. Thoha and Fajrin [16] have studied the manufacture of briquettes from teak leaves, but research on making briquettes from teak branches is still limited. Therefore, research about the manufacture of briquettes from teak branches is required.
In making briquettes, binder selection materials need to be considered. The binder material must have good adhesive properties, not reduce the thermal properties of the resulting briquettes, and be free of pollution [13]. Organic binders such as starch and molasses are preferred because of producing relatively little ash on briquette combustion [16].
Meanwhile, Aransiola et al. [17] observed the effect of binder type on briquettes from corncob. That study stated that cassava starch, corn starch, and gelatine could produce high-quality briquettes where the binder with cassava delivered products with better physical properties.
Therefore, in this research has carried out the manufacture of briquettes from teak branches using starch as a binder.
In this case, the quality of the briquettes would be observed based on the calorific value and water content due to the influence of particle size of carbonized biomass and the binder ratio in briquettes composition. In the previous study [18], it was said that these two parameters influenced the quality of the briquettes produced. The data obtained will be analyzed statistically using ANOVA.

Materials preparation
The teak branches were obtained from twoyear-old teak plants collected from Dawarblandong District. The components were cut into a size range of 3-5 cm (Fig. 1). The binder was tapioca flour dissolved with boiling distilled water at a ratio of 1:2 (gr/ml).

Processing the biobriquettes
The first step in the manufacture of biobriquette was the carbonization stage. At this stage, the teak tree branches were carbonized at a temperature of 300 o C for 3 hours to produce charcoal. Before further processing, an approximate analysis was carried out on the carbonized teak branches. The analysis results (Table 1) showed that charcoal was feasible as raw material with a relatively high carbon content of 62.5968%.  Furthermore, the charcoal (Fig. 2) was ground and sieved using five variations of sieve sizes, namely 30, 40, 50, 60, and 70 mesh. The next stage was mixing with the binder. Charcoal powder was mixed with tapioca paste under the variable values of 0.2; 0.4; 0.6; 0.8, and 1 (gr/gr) on the ratio of binder to biomass, where the mass of charcoal powder used was constant at 50 gr. The mixture was stirred until mixed well. After that, the following process was molding. The mixed dough was put into a cylinder molding with a diameter of 3.1 cm and a height of 3.4 cm, then compacted using a manual press. The last stage was drying.
The solidified bio-briquettes were removed from the mold and aired at room temperature for 24 hours. After that, a further drying process was carried out using an oven at a temperature of 105 o C for 5 hours. Thus the bio-briquettes of teak branches were obtained in Fig. 3.

Analysis
Research data collection was carried out with a complete randomized design so that the number of samples was 25 samples. The quality of biobriquettes was then analyzed by measuring the water content and calorific value of each samples product. The moisture content test was performed using the oven-dry method following the ASTM D-3173 standard [19], and the calorific value test using a bomb calorimeter by a standardized laboratory, Lab. Chem-Mix Primary. The data then were analyzed statistically using a two-way ANOVA using Minitab software.

Results and Discussion
The manufacture of bio-briquettes from teak branches with tapioca flour adhesive has been successfully performed. Data analysis of calorific value and moisture content samples were presented in interaction plots as shown in Fig. 4 and Fig. 5, respectively. In those figures, it can be seen that the graphs formed were linear lines. These represented no interaction between the particle size factor and the binder ratio to the two response variables, calorific value, and water content of the bio-briquettes in the specified parameters value range. The graph also showed that the increase in the ratio of binder to teak charcoal from 0.2 to 1 (gr/gr) was directly proportional to the increase in calorific value and moisture content of the bio-briquette samples. Meanwhile, the change in the charcoal particle size from 30 mesh to 70 mesh increased the calorific value of products but caused a decrease in the moisture content. The phenomenon was also described clearly on the main effect graphs, as shown in Fig. 6 and Fig.  7. The change in particle size and binder ratio resulted in an ascending line on the calorific value graph, while on the water content graph, the change in particle size formed a downward graph, and binder ratios formed an ascending graph. The larger the mesh size, the smaller the particle size. So it can be said that the smaller the particle size, the higher the calorific value of bio-briquettes but the lower the water content. Meanwhile, the greater the binder ratio, the greater the calorific value and moisture content of bio-briquettes. The phenomenon due to changes in particle size that occurred in this study was also reported by Ristianingsih et al. [18]. They stated that biomass in small size was preferred to manufacture biobriquette because it could produce products with a higher heating value due to a more extensive heat transfer cross-sectional area. Meanwhile, the phenomenon caused by the change in binder ratio in this study has similarities and differences with the observations made by Bazenet et al. [20] in making briquettes from rubberwood. That study stated that the addition of binder tapioca would reduce the heating value of the briquettes because it increased the moisture content of the sample. However, in this study, the more adhesives used in the briquette composition, the water content value increased, but the calorific value also increased. The phenomenon was slightly different from the theory that the higher the water content, the lower the calorific value. However, the graph in Fig. 6 more clearly displayed that particle size was more significant in influencing the calorific value than the binder ratio. It was shown from the vertical line of the graph formed by the change in the particle size to the calorific value, while the binder ratio tended to establish a sloping graph. In contrast, Fig. 7 showed that both particle size and binder ratio almost had the same effect on the moisture content value.
Statistically, when analyzed further, the analysis of variance (ANOVA) results ( Table 2 & Table 3) showed that the particle size factor and binder ratio had a p-value smaller than 0.05 for the response to heating value and moisture content. It meant these two parameters significantly affect the calorific value and water content. However, based on the higher value, the F-value of parameter particle size in the calorific value response was much higher (F-value = 669.3) than the F-value of the binder ratio (F-value = 18.4). In contrast, in the moisture content response, the F-value of binder ratio was slightly larger (F-value = 49.27) than the F-value of the particle size (F-value = 31.06). The data clarified that the particle size parameter had a much more significant effect on the calorific value than the binder ratio. Conversely, for the response value of the moisture content, the binder ratio parameter had a more substantial influence on the particle size.  Therefore, from the results of this study, it is suggested that for the manufacture of biobriquettes from teak branches with tapioca as the binder, even though an increase in the binder ratio increased the calorific value, the use of a smaller amount of binder and a smaller particle size (larger mesh) was more recommended. Further suggested that the next researcher can conduct research reviewing this statement from the economic analysis aspect.
Moreover, the bio-briquette produced in all variations of the parameters in this research had a calorific value of 5010.479 cal/gr -6037.611 cal/gr and a moisture content of 0.2207% -4.7001%. This value has met the applicable quality standards of briquettes (SNI 1/6235/2000), with a minimum calorific value of 5000 cal/gr and a maximum moisture content of 8% .

Conclusions
Bio-briquettes from teak branches could be prepared using tapioca as the binder. Observing the effect of particle size parameters and binder ratio for the range of values used, 30 -70 mesh and 0.2 -1 (gr/gr) obtained that the calorific value would increase along with the increase in particle mesh size (smaller particle size) and binder ratio, while the water content was getting smaller with smaller particle size, and getting bigger with higher binder ratio. The ANOVA results showed that these two factors significantly affected the resulting bio-briquette samples' heating value and moisture content. Furthermore, the statistical analysis results of this study suggested using biomass in small size and a small amount of adhesive in the manufacture of bio-briquettes. However, this study proposed to confim this statement based on economic point of view for future research. The bio-briquette calorific value and moisture content had met SNI 1/6235/2000.